OBSERVATIONS PERTAINING TO THE EFFECT OF CHEMICAL TRANSFORMATION IN-CLOUD ON THE ANTHROPOGENIC AEROSOL-SIZE DISTRIBUTION

Authors
Citation
Wr. Leaitch, OBSERVATIONS PERTAINING TO THE EFFECT OF CHEMICAL TRANSFORMATION IN-CLOUD ON THE ANTHROPOGENIC AEROSOL-SIZE DISTRIBUTION, Aerosol science and technology, 25(2), 1996, pp. 157-173
Citations number
37
Categorie Soggetti
Engineering, Mechanical","Environmental Sciences
ISSN journal
02786826
Volume
25
Issue
2
Year of publication
1996
Pages
157 - 173
Database
ISI
SICI code
0278-6826(1996)25:2<157:OPTTEO>2.0.ZU;2-5
Abstract
Airborne observations from two case studies of continental cloud, one of summertime cumulus and one of autumn stratus, are examined for evid ence of changes in the size of the accumulation-mode aerosol particles due to S(IV) oxidation in cloud. Such changes might affect the effici ency with which the aerosol scatters light and its ability to function as cloud condensation nuclei (CCN), and hence impact climate. In both cases, there were strong anthropogenic contributions to the aerosol, and the measured particles (0.17-2 mu m in diameter) were not scavenge d with 100% efficiency: the relative number concentrations of measured particles activated in cloud were about 70% for the cumulus and 15%-5 0% for the stratus. Within the measurement resolution, the apparent ef fect of cloud processing in the cumulus case was to nearly preserve th e shape of the size distribution of the measured aerosol, even after t he mass addition of sulfate by S(IV) oxidation. This can be accomplish ed through the activation of sufficiently small particles to balance t he increase in larger particles. In the stratus case, the aerosol size distributions associated with the cloud are bimodal with peaks at 0.2 3 and 0.35 mu m. The second peak coincides closely with the lower size of particles activated in the cloud suggesting that S(IV) oxidation o r possibly coalescence scavenging contributed to its formation.